Technical Field
The present invention relates to an optical signal transmission device and an electronic apparatus using the same that utilize optical signals to implement bidirectional signal transmission in applications such as rotating security cameras or between a rotating unit of an industrial robot and a fixed unit that supports the rotating unit, for example.
Background Art
Transmission of signals between components that rotate relative to one another, such as in rotating security cameras, has conventionally been achieved using slip rings that have mechanical contact points. FIG. 5 illustrates a conventional signal transmission device 200, in which a rotating unit 220 that can rotate about a rotary shaft 230 is arranged facing a fixed unit 210. The rotating unit 220 includes devices 222A and 222B such as a motor, a sensor, and a controller, and wires 224A and 224B that are connected to these devices 222A and 222B are connected to a plurality of slip rings 232 arranged around the periphery of the rotary shaft 230. The plurality of slip rings 232 respectively contact contact points 236 on the ends of brushes 234 to allow signals to be transmitted.
These slip rings 232 have a high probability of causing communication errors within a relatively short period of time due to factors such as accumulation of dust, corrosion, wear, and sliding instabilities in the contact points 236 and therefore present durability issues in terms of the need for regular inspections and replacements. Moreover, increasing data throughput or implementing bidirectional communications requires increasing the number of slip rings 232 and brushes 234, thereby resulting in significant increases in cost. Therefore, contactless communication schemes that utilize optical transmission have been proposed as a solution. Patent Document 1, for example, proposes an approach that involves compensating for insufficiencies in the amount of light received resulting from optical axis offsets due to rotation by arranging a plurality of light-emitting devices or light-receiving devices (see Patent Document 1, FIG. 1).
Another proposed approach involves arranging light-receiving devices on a rotary shaft and, using reflectors or the like, controlling the angle of emitted light emitted from light-emitting devices arranged outwards from the rotary shaft to stabilize the amount of light received by the light-receiving devices during rotation. Although this approach is effective, the precision required to install the reflectors or the like as well as to control the angles thereof presents challenges in terms of manufacturability. Moreover, the mechanisms for rotating the light-emitting devices in circular paths around the light-receiving devices on the rotary shaft tend to be relatively large rotary mechanisms having a diameter of at least twice the distance between the light-receiving devices and the light-emitting devices, which presents obstacles to achieving reductions in size or diameter. Patent Document 2 and Patent Document 3 propose yet another approach, in which light-receiving devices are arranged on a rotary shaft and light-emitting devices arranged outwards from the rotary shaft are arranged at prescribed inclinations so that the emitted light is received stably and consistently even when the light-receiving devices are rotating.